1. Field of the Invention
The present invention relates to an exhaust pipe joint assembly (i.e., a joint assembly for connecting exhaust pipes together) which is interposed in an exhaust-gas system mainly of an engine for a motor vehicle such that an exhaust pipe on an upstream side (hereinafter also called xe2x80x9can upstream exhaust pipexe2x80x9d) and an exhaust pipe on a downstream side (hereinafter also called xe2x80x9ca downstream exhaust pipexe2x80x9d) can be connected in a manner to be relatively displaceable by bending.
2. Description of Related Art
An exhaust pipe which is disposed in an exhaust-gas system of an engine for a motor vehicle receives the transmission of vibrations of the engine. The vibrations are in turn transmitted to a motor vehicle body through a supporting member of the exhaust pipe, thereby resulting in the occurrence of noises.
In order to solve this kind of problem, there has hitherto been known an exhaust pipe joint assembly having interposed in an exhaust-gas system of an engine a spherical joint (Japanese Published Examined Patent Application No. 58503/1990) or a joint made up of a bellows pipe (Japanese Published Examined Utility Model Registration Application No. 1347/1985). The vibrations transmitted to the exhaust pipe are thus absorbed by the displacement of the exhaust pipe joint assembly.
In order to efficiently absorb the vibrations transmitted to the exhaust pipe by a bending displacement of the exhaust pipe joint assembly, it is necessary to minimize a minimum torque at which the exhaust pipe joint assembly gives rise to the bending displacement (hereinafter called xe2x80x9ca starting torque to generate a bending displacementxe2x80x9d).
The above-described spherical joint is displaceable by bending in all bending directions. However, since spherical sliding surfaces of a sealing member (gasket) and of a spherical flange are being forcibly urged toward each other, a sliding resistance becomes large. As a result, the starting torque to generate a bending displacement is large. In addition, there were cases in which exhaust gases leaked to some extent through the in sliding surfaces.
On the other hand, the above-described joint made up of the bellows pipe has advantages in that it can be bent in all bending directions, that the starting torque to generate a bending displacement is small, and that there is no leakage of exhaust gases. However, when the engine largely moves due to a torque reaction force, inertia force, or the like, relative to the vehicle body, the amounts of extension and contraction as well as of bending of the bellows pipe becomes excessive if the bellows pipe is small in length. As a result, undue stresses are operated on the bellows pipe. Therefore, in order to secure a sufficient strength and durability of the bellows pipe that will not generate cracks or the like, it is necessary to form the bellows pipe to have a certain length. As a consequence, there is a problem in that the joint made up of the bellows pipe is inferior to the spherical joint in points of cost, weight, and space to be occupied thereby.
The present invention has an object of providing an exhaust pipe joint assembly which is free from the above-described problems while maintaining the above-described advantages of the joint made up of the bellows pipe.
In order to attain the above and other objects, the present invention is an exhaust pipe joint assembly which is interposed in an exhaust-gas system of an engine and which has a bellows pipe for connecting an upstream exhaust pipe and a downstream exhaust pipe, comprising: a first joint pipe connected to the upstream exhaust pipe and a second joint pipe connected to the downstream exhaust pipe, both the joint pipes being disposed so as to form a double pipe construction with the bellows pipe; a first pair of ball receiving portions disposed on a peripheral surface of the first joint pipe at a distance from each other in a circumferential direction and a second pair of ball receiving portions disposed on a peripheral surface of the second joint pipe at a distance from each other in the circumferential direction, the first pair of ball receiving portions and the second pair of ball receiving portions being disposed at an angular phase difference with each other in the circumferential direction; and a coupling piece having a pair of first ball joint portions engaged with the first pair of ball receiving portions of the first joint pipe respectively through a ball, and a pair of second ball joint portions engaged with the second pair of ball receiving portions of the second joint pipe respectively through a ball.
According to the present invention, the first joint pipe becomes displaceable relative to the coupling piece by rotation about a line connecting the pair of the first ball joint portions. Further, the second joint pipe becomes displaceable relative to the coupling piece by rotation about a line connecting the pair of the second ball joint portions. In addition, the first ball joint portions and the second ball joint portions have the same angular phase difference as that between the ball receiving portions of the first joint pipe and the ball receiving portions of the second joint pipe. As a result, the second joint pipe becomes displaceable relative to the first joint pipe by bending with a small starting torque in all directions. The advantages peculiar to the bellows pipe are thus not impaired. On the other hand, by means of each of the ball joint portions, the displacement in the longitudinal direction of each of the joint pipes relative to the coupling piece is restricted. Further, by the interference of the coupling piece with each of the joint pipes, the bending displacement of both the joint pipes is restricted to a predetermined range. Therefore, even if the engine largely moves relative to the vehicle body due to the torque reaction force, the inertia force, or the like, the amounts of extension and contraction as well as of bending are restricted to a predetermined range. As a result, undue stresses are not operated on the bellows pipe. Even if the bellows pipe is made smaller in length, there will occur no problem in strength and durability. The above-described problems relating to the bellows pipe will thus be solved.
Although the above-described exhaust pipe assembly according to the present invention is capable of being bent in all directions, the angular phase difference is preferably made to be 90xc2x0. The changes in the starting torque depending on the changes in the bending direction can advantageously be made smaller.
It is also possible to dispose the first ball joint portions and the second ball joint portions in the same position in the longitudinal direction of the joint pipes. In such as arrangement, however, it is necessary to form a large notch in the periphery of each of the joint pipes in a portion corresponding to the ball receiving portions of the other of the joint pipes in order to avoid interference of the two joint pipes. As a result, the rigidity of the joint pipes becomes lower and there is a possibility that the joint pipes and the coupling piece become rickety. As a solution, preferably, the first ball joint portions and the second ball joint portions are disposed at a distance from each other in the longitudinal direction of the joint pipes. Then, there is no need of forming the notch in the periphery of the joint pipe. Even if there is such a need, the notch may be kept small to the extent possible. Therefore, the rigidity of the joint pipes can be secured and the disadvantage in that the joint pipes and the coupling piece become rickety can be prevented.
Still furthermore, although it is possible to dispose both the joint pipes and the coupling piece outside the bellows pipe, preferably both the joint pipes and the coupling piece are disposed inside the bellows pipe in order to protect the ball joint portions from foreign substances such as dirts, water, or the like.